Spindle motor and disk drive apparatus

ABSTRACT

A spindle motor includes a stationary portion and a rotating portion. The rotating portion includes a magnet arranged around a central axis extending in a vertical direction. The stationary portion includes a base member and a magnetic member arranged below the magnet and fixed to the base member. The base member includes an upper surface extending out perpendicularly or substantially perpendicularly to the central axis, and a wall surface extending in an axial direction. The magnetic member includes an annular plate portion arranged on the base member and a projecting portion arranged to extend downward from the plate portion. At least a portion of the projecting portion is arranged to be in contact with the wall surface. An adhesive is arranged between the plate portion and the upper surface of the base member and between the projecting portion and the wall surface.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a spindle motor and more specificallyto a spindle motor used in a disk drive apparatus.

2. Description of the Related Art

Hard disk apparatuses and optical disk apparatuses are typicallyprovided with a spindle motor to rotate a disk about a central axis.Such spindle motors include a stationary portion fixed to a housing ofthe apparatus, and a rotating portion arranged to rotate whilesupporting the disk. The spindle motor is arranged to produce a torquecentered on the central axis by a magnetic flux generated between thestationary and rotating portions that works to rotate the rotatingportion with respect to the stationary portion.

Some known spindle motors include a magnetic member arranged to attractthe rotating portion toward the stationary portion. Such a magneticmember is typically fixed to the stationary portion to produce axialmagnetic attraction between it and a magnet provided in the rotatingportion. JP-A 2001-309605, for example, describes a conventionalmagnetic ring attached to a stationary member to apply a downward axialforce to a rotor. JP-A 2007-43893, for example, also describes aconventional motor including a ring-shaped magnetic attraction ringfixed to a bottom surface of a motor base.

Concerning a method of fixing such a magnetic member to the stationaryportion, paragraph [0034] of JP-A 2001-309605 includes the followingexplanation: “ . . . the magnetic ring 42 is adhered to the stationarymember 21, for example, through an adhesive”. This adhesive, however,may deteriorate with a long-term use due to influence of changes inambient temperature and the like which will result in a reduction infixing strength of the adhesive. Since magnetic attraction constantlyacts between the magnetic ring and the magnet, the deterioration of theadhesive may lead to a displacement of the magnetic ring toward themagnet. Therefore, the type of the adhesive and the amount of theadhesive applied need to be determined appropriately, with the long-termdeterioration of the adhesive taken into consideration, to maintain asufficient fixing strength of the adhesive.

Meanwhile, claim 1 of JP-A2007-43893 describes the following feature:“the attraction ring has a plurality of radially-projecting projectingportions defined in an outer circumferential portion or an innercircumferential portion thereof, and the projecting portions are pressfitted to a wall portion provided in the motor base and arranged toproject from the bottom surface thereof in an axial direction, so as tobe fixed to the motor base”. The technique described in JP-A 2007-43893,however, has a problem in that a stress that accompanies the pressfitting acts on the entire attraction ring. Therefore, the press fittingmay lead to a deformation of the attraction ring as a whole. Thedeformation of the attraction ring results in variations in the axialdistance between the magnet and the attraction ring. This may lead tocontact between the magnet and the attraction ring, and the occurrenceof undesirable vibrations due to uneven magnetic attraction, or thelike.

SUMMARY OF THE INVENTION

A spindle motor according to a preferred embodiment of the presentinvention includes a stationary portion and a rotating portion. Therotating portion includes a magnet arranged around a central axisextending in a vertical direction. The stationary portion includes abase member and a magnetic member arranged below the magnet and fixed tothe base member.

The base member includes an upper surface extending out perpendicularlyor substantially perpendicularly to the central axis, and a wall surfaceextending in an axial direction. The magnetic member preferably includesan annular plate portion arranged on the upper surface of the basemember and a projecting portion arranged to extend downward from theplate portion.

At least a portion of the projecting portion is preferably arranged tobe in contact with the wall surface. The stationary portion preferablyfurther includes an adhesive arranged between the plate portion and theupper surface of the base member and between the projecting portion andthe wall surface.

The above and other features, elements, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of preferred embodiments of the presentinvention with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial vertical cross-sectional view of a spindle motoraccording to a preferred embodiment of the present invention.

FIG. 2 is a vertical cross-sectional view of a disk drive apparatusaccording to a preferred embodiment of the present invention.

FIG. 3 is a vertical cross-sectional view of a spindle motor accordingto a preferred embodiment of the present invention.

FIG. 4 is a partial vertical cross-sectional view of the spindle motor.

FIG. 5 is a partial vertical cross-sectional view of a stationaryportion according to a preferred embodiment of the present invention.

FIGS. 6 and 7 are each a perspective view of a thrust yoke according toa preferred embodiment of the present invention.

FIGS. 8, 9, and 10 are each a partial vertical cross-sectional view of astationary portion according to a preferred embodiment of the presentinvention.

FIGS. 11 and 12 are each a partial vertical cross-sectional view of aspindle motor according to a preferred embodiment of the presentinvention.

FIG. 13 is a vertical cross-sectional view of a spindle motor accordingto a preferred embodiment of the present invention.

FIG. 14 is a partial vertical cross-sectional view of the spindle motor.

FIG. 15 is a partial top view of a thrust yoke according to a preferredembodiment of the present invention.

FIGS. 16, 17, and 18 are each a partial vertical cross-sectional view ofa stationary portion according to a preferred embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings. It is assumedherein that a vertical direction is defined as a direction in which acentral axis extends, and that a side on which a magnet is located withrespect to a magnetic member is defined as an upper side. The shape ofeach member and relative positions of different members will bedescribed based on this assumption. It should be noted, however, thatthe above definitions of the vertical direction and the upper and lowersides are simply applied to facilitate the description provided herein,and should not be construed to restrict in any way the orientation of aspindle motor or a disk drive apparatus according to any preferredembodiment of the present invention when in actual use.

FIG. 1 is a partial vertical cross-sectional view of a spindle motor 102according to a preferred embodiment of the present invention. Asillustrated in FIG. 1, the spindle motor 102 includes a stationaryportion 103 and a rotating portion 104. The rotating portion 104 issupported to be rotatable with respect to the stationary portion 103.

The rotating portion 104 includes a magnet 143 arranged around a centralaxis 109 extending in the vertical direction. The stationary portion 103includes a base member 131 and a magnetic member 134. The magneticmember 134 is arranged below the magnet 143 and fixed to the base member131.

The base member 131 includes an upper surface 151 spreadingperpendicularly to the central axis 109, and a wall surface 153extending in an axial direction. The magnetic member 134 includes aplate portion 134 a and a projecting portion 134 b. The magnetic member134 preferably includes a plate portion 134 a and a projecting portion134 b. The plate portion 134 a includes an annular portion arranged onthe upper surface 151 of the base member 131. The projecting portion 134b includes a portion extending from the plate portion 134 a in the axialdirection.

In the spindle motor 102, at least a portion of the projecting portion134 b is preferably press fitted to the wall surface 153 of the basemember 131. Therefore, the strength of the connection by which themagnetic member 134 is fixed to the base member 131 is less likely tosignificantly decrease due to a long-term use than when they are fixedto each other with only an adhesive. Moreover, because only theprojecting portion 134 b is press fitted to the wall surface 153, adeformation due to the press fitting is unlikely to occur to the plateportion 134 a of the magnetic member 134.

Next, a preferred embodiment of the present invention will be describedmore specifically.

FIG. 2 is a vertical cross-sectional view of a disk drive apparatus 1according to a first preferred embodiment of the present invention. Thedisk drive apparatus 1 is preferably designed to read and writeinformation from or to a magnetic disk 12 (hereinafter referred tosimply as the “disk 12”) while rotating the disk 12 about a central axis9. As illustrated in FIG. 2, the disk drive apparatus 1 preferablyincludes an apparatus housing 11, the disk 12, an access portion 13, anda spindle motor 2.

The apparatus housing 11 is arranged to contain the disk 12, the accessportion 13, and the spindle motor 2. An upper portion of the apparatushousing 11 is preferably closed with a cover portion 11 a. The accessportion 13 is designed to read and write information from or to the disk12 while moving a head 13 a along a recording surface of the disk 12supported by the spindle motor 2. Note that the access portion 13 may bedesigned to perform only one of reading and writing of information fromor to the disk 12.

Next, the structure of the spindle motor 2 will now be described below.FIG. 3 is a vertical cross-sectional view of the spindle motor 2. Asillustrated in FIG. 3, the spindle motor 2 includes a stationary portion3 and a rotating portion 4. The stationary portion 3 is fixed to theapparatus housing 11 of the disk drive apparatus 1. The rotating portion4 is supported to be rotatable with respect to the stationary portion 3.

The stationary portion 3 preferably includes a base member 31, astationary bearing unit 32, a stator unit 33, and a thrust yoke 34.

The base member 31 defines a portion of the apparatus housing 11 of thedisk drive apparatus 1, and the base member 31 and a remaining portionof the apparatus housing 11 are together defined by a single member. Theapparatus housing 11, including the base member 31, is produced, forexample, by making an aluminum casting and subjecting this casting to acutting process. In addition, a large area in a surface of the apparatushousing 11 is coated with an electrodeposition coating layer 31 f toprevent dust from gathering. The base member 31 preferably includes acylindrical portion 31 a, a bottom portion 31 b, a yoke receivingportion 31 c, and an outside portion 31 d.

The cylindrical portion 31 a includes a portion projecting upward from aradially inner edge portion of the bottom portion 31 b. Hereinafter, theterms “radially”, “radial”, and “radial direction” refer to directionsperpendicular or substantially perpendicular to the central axis. Thebottom portion 31 b includes a substantially disc-shaped portionextending radially outward from a lower end portion of the cylindricalportion 31 a. The yoke receiving portion 31 c includes a portionarranged radially outward of the bottom portion 31 b and to which thethrust yoke 34 is fixed. The outside portion 31 d includes a portionarranged radially outward of the yoke receiving portion 31 c andextending upward and radially outward therefrom.

The bottom portion 31 b, the yoke receiving portion 31 c, and theoutside portion 31 d of the base member 31 preferably together define anaccommodating portion 31 e which is substantially in the shape of a cupopening upward. The stationary bearing unit 32, the stator unit 33, thethrust yoke 34, and the rotating portion 4 are placed inside theaccommodating portion 31 e.

Note that the base member 31 and the apparatus housing 11 may be definedby separate members if so desired.

The stationary bearing unit 32 is a mechanism to rotatably support ashaft 41 provided in the rotating portion 4. The stationary bearing unit32 is fixed to an inside surface of the cylindrical portion 31 a of thebase member 31. The stationary bearing unit 32 preferably includes asubstantially cylindrical sleeve 32 a and a cap 32 b arranged to close alower opening of the sleeve 32 a. A clearance space between an innercircumferential surface of the sleeve 32 a and an outer circumferentialsurface of the shaft 41 is filled with lubricating oil.

The stator unit 33 preferably includes a stator core 35 and a pluralityof coils 36. The stator unit 33 is designed to generate magnetic flux inaccordance with drive currents supplied to the coils 36.

The stator core 35 preferably includes an annular core back 35 a and aplurality of tooth portions 35 b arranged to project radially outwardfrom the core back 35 a. The core back 35 a is fixed to an outercircumferential surface of the cylindrical portion 31 a of the basemember 31. The stator core 35 is produced, for example, by subjecting anelectromagnetic steel sheet to a stamping process to obtain a pluralityof electromagnetic steel sheet stampings in the aforementioned shape,and placing the stampings one upon another in an axial direction.

Each coil 36 is preferably defined by a lead wire wound around aseparate one of the tooth portions 35 b of the stator core 35. The coils36 are positioned above the bottom portion 31 b of the base member 31.

The thrust yoke 34 is arranged below a rotor magnet 43 described below,and fixed to the yoke receiving portion 31 c of the base member 31. Thethrust yoke 34 is made of a magnetic substance, examples of whichinclude an electromagnetic steel sheet (e.g., a silicon steel sheet,etc.), ferromagnetic stainless steel (e.g., SUS430, etc.), and acold-rolled steel sheet (e.g., SPCC, SPCE, etc.). The thrust yoke 34corresponds to a magnetic member. The thrust yoke 34 is arranged toattract the rotating portion 4 toward the stationary portion 3 bymagnetic attraction generated between the thrust yoke 34 and the rotormagnet 43 to stabilize the posture of the rotating portion 4 duringrotation.

The rotating portion 4 preferably includes the shaft 41, a hub 42, andthe rotor magnet 43.

The shaft 41 is substantially in the shape of a column, and is arrangedto extend in the vertical direction along the central axis 9. The shaft41 is inserted inside the sleeve 32 a, and supported to be rotatablewith respect to the stationary bearing unit 32. The hub 42 is fixed tothe shaft 41, and arranged to rotate together with the shaft 41. The hub42 includes a support surface to support the disk 12. Note that the hub42 and the shaft 41 may be defined by a single member if so desired.

The rotor magnet 43 is fixed to the hub 42. The rotor magnet 43 isannular in shape and centered on the central axis 9. That is, the rotormagnet 43 is arranged around the central axis 9. An innercircumferential surface of the rotor magnet 43 is arranged radiallyopposite the tooth portions 35 b and the coils 36 with a gaptherebetween. In addition, the inner circumferential surface of therotor magnet 43 defines a pole surface on which north and south polesalternate with each other.

When the drive currents are supplied to the coils 36 of the stator unit33 of the spindle motor 2, radial magnetic flux is generated about thetooth portions 35 b of the stator core 35. As a result, interactionbetween the magnetic flux about the tooth portions 35 b and magneticflux from the rotor magnet 43 produces a circumferential torque to causethe rotating portion 4 to rotate about the central axis 9 with respectto the stationary portion 3. The disk 12 supported by the hub 42 rotatesabout the central axis 9 together with the shaft 41 and the hub 42.

Next, the fixing of the thrust yoke 34 to the base member 31 will now bedescribed in more detail below. FIG. 4 is a partial verticalcross-sectional view of the spindle motor 2, in which the thrust yoke 34is shown. FIG. 5 is a partial vertical cross-sectional view of thestationary portion 3, illustrating the thrust yoke 34 and its vicinitiesin more enlarged form. FIG. 6 is a perspective view of the thrust yoke34.

As illustrated in FIGS. 4 and 5, an upper surface 51 of the yokereceiving portion 31 c of the base member 31 preferably includes anannular flat surface spreading perpendicularly or substantiallyperpendicularly to the central axis 9. The upper surface 51 of the yokereceiving portion 31 c is positioned at a level higher than that of anupper surface 52 of the bottom portion 31 b. A cylindrical wall surface53 is arranged to extend between the upper surface 52 of the bottomportion 31 b and the upper surface 51 of the yoke receiving portion 31c. The wall surface 53 is arranged to extend downward from a radiallyinner edge portion of the upper surface 51 of the yoke receiving portion31 c.

As illustrated in FIGS. 4 to 6, the thrust yoke 34 includes a plateportion 34 a and a projecting portion 34 b. The plate portion 34 aincludes an annular portion arranged on the upper surface 51 of the yokereceiving portion 31 c to extend perpendicularly or substantiallyperpendicularly to the central axis 9. An upper surface of the plateportion 34 a is arranged axially opposite a lower surface of the rotormagnet 43 with a gap therebetween. The projecting portion 34 b includesa substantially cylindrical portion extending downward from a radiallyinner edge portion of the plate portion 34 a. An outer circumferentialsurface of the projecting portion 34 b is arranged radially opposite thewall surface 53 of the base member 31.

The outer circumferential surface of the projecting portion 34 b has aplurality of raised portions 61 arranged thereon. In the presentpreferred embodiment, the raised portions 61 are arranged at regularintervals in a circumferential direction. Each of the raised portions 61is arranged to bulge radially outward from the radially outercircumferential surface of the projecting portion 34 b. The projectingportion 34 b of the thrust yoke 34 is press fitted to the base member 31with the raised portions 61 in contact with the wall surface 53.

In order to obtain a high fixing strength as a result of the pressfitting, it is preferable that a radial press-fit interference(allowance) for the press fitting of the thrust yoke 34 to the basemember 31 be about 5 μm or more, for example. Moreover, the radialpress-fit interference for the press fitting of the thrust yoke 34 tothe base member 31 is preferably about 50 μm or less, more preferablyabout 35 μm or less, for example, to increase the ease of the pressfitting.

Each raised portion 61 preferably includes a curved surface 61 a. In thepresent preferred embodiment, as illustrated in FIG. 5, the surface 61 aof each raised portion 61 is preferably in the shape of a smooth curvein a vertical cross-section. Therefore, it is possible to press fit theraised portions 61 to the wall surface 53 of the base member 31 with asmall press-fit force during a production process.

In addition, an adhesive 62 is preferably arranged between the basemember 31 and the thrust yoke 34. The adhesive 62 contributes to thestrength with which the base member 31 and the thrust yoke 34 are fixedto each other. That is, the base member 31 and the thrust yoke 34 arefixed to each other by a combination of the press fitting and theadhesive 62, for example. Accordingly, the base member 31 and the thrustyoke 34 are fixed to each other more securely than when they are fixedto each other by only one of the press fitting and the adhesive 62.

The adhesive 62 may deteriorate with long-term use, due to influence ofchanges in ambient temperature and the like, resulting in a decrease inthe fixing strength. In the present preferred embodiment, however, aportion of the fixing strength owing to the press fitting will bemaintained even after the deterioration of the adhesive 62. Thiscontributes to reducing the probability of the thrust yoke 34 coming offthe base member 31 due to the magnetic attraction between the thrustyoke 34 and the rotor magnet 43 after the deterioration of the adhesive62.

Moreover, in the present preferred embodiment, a fixing strengthrequired for the fixing of the thrust yoke 34 to the base member 31 doesnot need to be accomplished by only the adhesive 62. This leads to anincreased number of options for the choice of the adhesive 62. It makesit possible, for example, to choose an adhesive that takes a relativelylong time to solidify as the adhesive 62, in order to facilitate anoperation of application of the adhesive 62.

Moreover, in the present preferred embodiment, the projecting portion 34b, which is arranged to extend in the axial direction from the plateportion 34 a of the thrust yoke 34, is press fitted to the wall surface53 of the base member 31. Therefore, a stress applied from the wallsurface 53 during the press fitting is unlikely to reach the plateportion 34 a of the thrust yoke 34. This reduces the probability of adeformation of the plate portion 34 a. Furthermore, in the spindle motor2 according to the present preferred embodiment, the axial distancebetween the plate portion 34 a and the rotor magnet 43 is unlikely tovary at different positions.

In the present preferred embodiment, it is preferable that, only theraised portions 61 be arranged in contact with the wall surface 53within the outer circumferential surface of the projecting portion 34 b.Because the raised portions 61 are arranged discontinuously in thecircumferential direction, the press fitting of the projecting portion34 b to the wall surface 53 is easily achieved even when the dimensionsof the projecting portion 34 b or those of the wall surface 53 of thebase member 31 are not highly precise. In particular, in the case wherethe thrust yoke 34 is produced by a press molding process, variationsare more likely to occur in circularity of the projecting portion 34 bthan in the case where the thrust yoke 34 is produced by another method,such as a cutting process. In the present preferred embodiment, thepress fitting of the projecting portion 34 b to the wall surface 53 iseasily achieved even when the projecting portion 34 b has a low degreeof circularity.

Furthermore, the stress applied from the wall surface 53 during thepress fitting acts primarily on the raised portions 61 within the outercircumferential surface of the projecting portion 34 b, so that theprobability of a deformation of the projecting portion 34 b as a wholeis reduced. This leads to an additional reduction in the probability ofa deformation of the plate portion 34 a.

A concavity portion 63 is preferably defined in an inner circumferentialsurface of the projecting portion 34 b at a position corresponding toeach raised portion 61. It is possible to form the concavity portion 63at a position opposite to each raised portion 61 at the same time whenthe raised portions 61 are formed by press working, for example. Whenthe thrust yoke 34 is press fitted to the base member 31, an operator isable to recognize locations of the raised portions 61 by viewing theconcavity portions 63. This facilitates the press fitting operation.

As illustrated in FIGS. 3 and 4, a surface of the outside portion 31 dof the base member 31 is, except some portions thereof, coated with theelectrodeposition coating layer 31 f. The electrodeposition coatinglayer 31 f contributes to preventing gathering of dust from a metalsurface subjected to a cutting process.

Meanwhile, neither the wall surface 53 nor the upper surface 51 of theyoke receiving portion 31 c is coated with the electrodeposition coatinglayer 31 f. That is, both the wall surface 53 and the upper surface 51of the yoke receiving portion 31 c have their metal surfaces subjectedto a cutting process left exposed. As these metal surfaces determine theradial and axial positions of the thrust yoke 34, the exposure of themetal surfaces contributes to increasing the precision of the relativeposition of the thrust yoke 34 with respect to the base member 31.

Note that the upper surface 51 of the yoke receiving portion 31 c mayhave the entirety of its metal surface left exposed as illustrated inFIGS. 4 and 5, or may alternatively have its metal surface left exposedonly at a portion thereof positioned below the plate portion 34 a of thethrust yoke 34.

Next, various examples of a modifications of the first preferredembodiment will now be described below with a focus on differences fromthe above-described preferred embodiment.

FIG. 7 is a perspective view of a thrust yoke 234 according to anexample of a modification of the first preferred embodiment. In theexample of a modification illustrated in FIG. 7, a plurality of notches264 are defined in a projecting portion 234 b of the thrust yoke 234.Each of the notches 264 is arranged to extend axially upward from alower end portion of the projecting portion 234 b, and extend throughoutthe projecting portion 234 b in the radial direction.

In the example of a modification illustrated in FIG. 7, each pair of twoof the notches 264 are arranged to have a raised portion 261 nearbytherebetween. A portion of the projecting portion 234 b which ispositioned between the two notches 264 defining each pair has anincreased flexibility as compared to when no notches 264 are provided.In other words, an elastic section 265 including one of the raisedportions 261 is defined between the two notches 264 forming each pair.

When the thrust yoke 234 is press fitted to a base member, it ispossible to cause each elastic section 265 to bend radially inward bybringing the raised portion 261 therein into contact with a wall surfaceof the base member. This contributes to preventing a deformation of theother portions of the thrust yoke 234 than the elastic sections 265.Moreover, the radially inward bending of the elastic sections 265contributes to preventing the base member from being scraped with theraised portions 261 during the press fitting. Thus, it is possible toprevent dust from being generated from the base member 231 whileensuring a sufficient fixing strength by the press fitting.

Note that the notches 264 may preferably be arranged in pairs such thatthe two notches 264 forming each pair are arranged on eithercircumferential side of and close to a separate one of the raisedportions 261, and that the notches 264 may alternatively be arrangedsuch that each notch 264 is provided on one side of and close to aseparate one of the raised portions 261. When at least one notch 264 isdefined in the vicinity of each raised portion 261, portions of theprojecting portion 234 b which are in the vicinity of the notches 264increase in flexibility. This contributes to preventing a deformation ofthe other portions of the thrust yoke 234 during the press fitting.

FIG. 8 is a partial vertical cross-sectional view of a stationaryportion 303 according to another example of a modification of the firstpreferred embodiment. In the example of a modification illustrated inFIG. 8, a recessed portion(s) 354 is defined in a wall surface 353 of abase member 331, and raised portions 361 of a thrust yoke 334 arearranged in contact with the recessed portion(s) 354. The raisedportions 361 are thus engaged with the recessed portion(s) 354,resulting in an increase in the strength with which the thrust yoke 334is fixed to the base member 331.

Note that the recessed portion(s) 354 may be defined by an annulargroove extending continuously around an entire circumference of the wallsurface 353, or may alternatively be defined in the wall surface 353only at positions corresponding to the raised portions 361. In the casewhere the recessed portion(s) 354 is defined by an annular grooveextending continuously around the entire circumference of the wallsurface 353, it is not necessary to adjust circumferential positions ofthe raised portions 361 when press fitting the thrust yoke 334 to thebase member 331. This facilitates the operation of press fitting thethrust yoke 334 to the base member 331.

FIG. 9 is a partial vertical cross-sectional view of a stationaryportion 403 according to yet another example of a modification of thefirst preferred embodiment. In the example of a modification illustratedin FIG. 9, first and second raised portions 461 a and 461 b, one spacedfrom the other in the axial direction, are defined in a projectingportion 434 b of a thrust yoke 434. That is, in the example of amodification illustrated in FIG. 9, the thrust yoke 434 includes thefirst and second raised portions 461 a and 461 b, and the first andsecond raised portions 461 a and 461 b are arranged at different axialpositions. This arrangement contributes to increasing the strength withwhich the projecting portion 434 b is fixed to a wall surface 453.

Note that the first and second raised portions 461 a and 461 b may bearranged at the same circumferential position as illustrated in FIG. 9,or may alternatively be arranged at different circumferential positions.

FIG. 10 is a partial vertical cross-sectional view of a stationaryportion 503 according to yet another example of a modification of thefirst preferred embodiment. In the example of a modification illustratedin FIG. 10, a raised portion 555 is defined in a wall surface 553 of abase member 531. In addition, a projecting portion 534 b of a thrustyoke 534 is press fitted to the wall surface 553 with the raised portion555 arranged in contact with an outer circumferential surface of theprojecting portion 534 b.

FIG. 11 is a partial vertical cross-sectional view of a spindle motor602 according to yet another example of a modification of the firstpreferred embodiment. In the example of a modification illustrated inFIG. 11, a groove 656 is defined between a bottom portion 631 b and ayoke receiving portion 631 c of abase member 631. A radially inner endsurface of the groove 656 defines a wall surface 653 extending in theaxial direction. Moreover, in the example of a modification illustratedin FIG. 11, a plurality of raised portions 661 are defined in an innercircumferential surface of a projecting portion 634 b of a thrust yoke634. The projecting portion 634 b of the thrust yoke 634 is press fittedto the base member 631 with the raised portions 661 arranged in contactwith the wall surface 653.

In the example of a modification illustrated in FIG. 11, an adhesive 662can be held within the groove 656 of the base member 631 to achieve anincrease in the fixing strength by the adhesive 662.

FIG. 12 is a partial vertical cross-sectional view of a spindle motor702 according to yet another example of a modification of the firstpreferred embodiment. In the example of a modification illustrated inFIG. 12, an upper surface 752 of a bottom portion 731 b and an uppersurface 751 of a yoke receiving portion 731 c together define acontinuous flat surface. A wall surface 753 is arranged to extend upwardfrom a radially outer edge portion of the yoke receiving portion 731 c.In the example of a modification illustrated in FIG. 12, a projectingportion 734 b of a thrust yoke 734 is arranged to extend upward from aradially outer edge portion of a plate portion 734 a of the thrust yoke734. A plurality of raised portions 761 are defined in an outercircumferential surface of the projecting portion 734 b. The projectingportion 734 b of the thrust yoke 734 is press fitted to a base member731 with the raised portions 761 arranged in contact with the wallsurface 753.

As is apparent from the foregoing description, the projecting portion ofthe thrust yoke may be arranged to extend either axially upward oraxially downward from the plate portion. Note, however, that when theprojecting portion is arranged to extend axially downward from the plateportion, a greater degree of flexibility is obtained in the arrangementof other members above the thrust yoke and in the design of thedimensions of such other members. For example, it is made easy toarrange the rotor magnet of the rotating portion close to the plateportion of the thrust yoke.

Note that the raised portions may be arranged only partially around thecircumference as in the above-described first preferred embodiment, andthat the raised portions may alternatively be substituted with anannular raised portion arranged to extend continuously around the entirecircumference. Furthermore, the projecting portion of the thrust yokemay be in the shape of a cylinder as in the above-described firstpreferred embodiment, or may alternatively be substituted with one ormore axial projections provided at one or more circumferentialpositions. Furthermore, the wall surface of the base member may be acylindrical surface as in the above-described first preferredembodiment, or may alternatively be substituted with one or moresurfaces provided at one or more circumferential positions.

Note that the thrust yoke may be fixed to the base member only throughthe press fitting, without use of an adhesive.

Also note that, without the projecting portion having any raisedportion, the outer circumferential surface or the inner circumferentialsurface of the projecting portion may be press fitted to the wallsurface at the entire circumference. That is, it is enough that at leasta portion of the projecting portion be press fitted to the wall surface.

Next, a second preferred embodiment of the present invention will now bedescribed below. The structure of a disk drive apparatus according tothe second preferred embodiment is similar to that of the disk driveapparatus 1 according to the first preferred embodiment, and redundantdescriptions will therefore be omitted.

FIG. 13 is a vertical cross-sectional view of a spindle motor 802according to the second preferred embodiment. As illustrated in FIG. 13,the spindle motor 802 includes a stationary portion 803 fixed to theapparatus housing of the disk drive apparatus, and a rotating portion804 arranged to rotate about a central axis 809 while supporting a disk812.

The stationary portion 803 preferably includes a base member 831, astator unit 832, a circuit board 833, a thrust yoke 834, an insulationsheet 835, and a stationary bearing unit 836.

The base member 831 defines a portion of the apparatus housing of thedisk drive apparatus, and the base member 831 and a remaining portion ofthe apparatus housing are together defined by a single member. The basemember 831 preferably includes a cylindrical portion 831 a, a bottomportion 831 b, a wall portion 831 c, and an outer plate portion 831 d.The cylindrical portion 831 a preferably includes a portion projectingupward from an inner edge portion of the bottom portion 831 b. Thebottom portion 831 b preferably includes a substantially disc-shapedportion extending radially outward from a lower end portion of thecylindrical portion 831 a. The wall portion 831 c preferably includes aportion extending radially outward and obliquely upward from an outeredge portion of the bottom portion 831 b. The outer plate portion 831 dpreferably includes a portion extending radially outward from an outeredge portion of the wall portion 831 c.

The bottom portion 831 b and the wall portion 831 c of the base member831 together define an accommodating portion 831 e which issubstantially in the shape of a cup opening upward. The stator unit 832,the thrust yoke 834, the insulation sheet 835, and a rotor magnet 843described below are placed inside the accommodating portion 831 e.Meanwhile, the circuit board 833 is arranged radially outside theaccommodating portion 831 e. In the spindle motor 802, the stator unit832 and the circuit board 833 are preferably arranged so as not tooverlap with each other in the axial direction, and arranged atsubstantially similar levels. This contributes to reducing the axialthickness of the spindle motor 802 as a whole.

Note that the base member 831 may be defined by a portion of theapparatus housing as in the present preferred embodiment, but mayalternatively be defined by a member separate from the apparatushousing.

The stator unit 832 includes a stator core 837 and a plurality of coils838. The stator unit 832 is designed to generate magnetic flux inaccordance with drive currents supplied to the coils 838. The statorcore 837 includes an annular core back 837 a and a plurality of toothportions 837 b arranged to project radially outward from the core back837 a. The core back 837 a is fixed to an outer circumferential surfaceof the cylindrical portion 831 a of the base member 831. The stator core837 is produced, for example, by subjecting an electromagnetic steelsheet to a stamping process to obtain a plurality of electromagneticsteel sheet stampings in the aforementioned shape, and placing thestampings one upon another in the axial direction.

Each of the coils 838 is preferably defined by a lead wire wound arounda separate one of the tooth portions 837 b of the stator core 837. Thecoils 838 are positioned above the bottom portion 831 b of the basemember 831. The coils 838 according to the present preferred embodimentare defined by three lead wires 838 a each arranged to supply anindividual phase of a three-phase alternating current. An input-side endportion of each of the three lead wires 838 a is drawn through a throughhole 831 f defined in the bottom portion 831 b to extend along a lowersurface of the bottom portion 831 b.

The circuit board 833 is preferably a board on which an electroniccircuit designed to supply the drive currents to the coils 838 ismounted. The circuit board 833 according to the present preferredembodiment is defined by a flexible printed circuit (FPC) board, whichis capable of bending. The circuit board 833 is preferably fixed to anoutside surface of the wall portion 831 c and a lower surface of theouter plate portion 831 d of the base member 831 through, for example,an adhesive or other fixing method. A solder portion 833 a is arrangedon a portion of the circuit board 833 which is fixed to the wall portion831 c. The input-side end portions of the lead wires 838 a drawn fromthe coils 838 are connected to the solder portion 833 a.

The thrust yoke 834 is press fitted to an inside surface of the wallportion 831 c of the base member 831, and also fixed to an upper surfaceof the bottom portion 831 b through an adhesive. An upper surface of thethrust yoke 834 is arranged axially opposite a lower surface of therotor magnet 843 described below with a gap therebetween. That is, thethrust yoke 834 is arranged below the rotor magnet 843. The thrust yoke834 is made of a magnetic substance, examples of which include anelectromagnetic steel sheet (e.g., a silicon steel sheet, etc.),ferromagnetic stainless steel (e.g., SUS430, etc.), and a cold-rolledsteel sheet (e.g., SPCC, SPCE, etc.). The thrust yoke 834 is arranged tocorrespond to the magnetic member. The thrust yoke 834 is preferablymade of a soft magnetic material. The thrust yoke 834 is arranged toattract the rotating portion 804 toward the stationary portion 803 bymagnetic attraction generated between the thrust yoke 834 and the rotormagnet 843 to stabilize the posture of the rotating portion 804 duringrotation.

The insulation sheet 835 is a sheet having an insulating property, andis arranged between the bottom portion 831 b of the base member 831 andthe coils 838. A polyethylene terephthalate (PET) film or the like, forexample, is used as the insulation sheet 835. The insulation sheet 835is arranged to prevent an undesirable electrical connection between thecoils 838 and the bottom portion 831 b of the base member 831. Theintervention of the insulation sheet 835 therebetween enables the coils838 and the bottom portion 831 b of the base member 831 to be arrangedclose to each other in the axial direction. This contributes to afurther reduction in the total axial thickness of the spindle motor 802.

The stationary bearing unit 836 is a mechanism to rotatably support ashaft 841 provided in the rotating portion 804. The stationary bearingunit 836 is fixed to an inside surface of the cylindrical portion 831 aof the base member 831. The stationary bearing unit 836 preferablyincludes a substantially cylindrical sleeve 836 a and a cap 836 barranged to close a lower opening of the sleeve 836 a. A clearance spacebetween an inner circumferential surface of the sleeve 836 a and anouter circumferential surface of the shaft 841 is filled withlubricating oil.

The rotating portion 804 preferably includes the shaft 841, a hub 842,and the rotor magnet 843.

The shaft 841 is provided substantially in the shape of a column, and isarranged to extend in the vertical direction along the central axis 809.The shaft 841 is inserted inside the sleeve 836 a, and supported to berotatable with respect to the stationary bearing unit 836. The hub 842is fixed to the shaft 841, and arranged to rotate together with theshaft 841. The hub 842 includes a support surface arranged to supportthe disk 812. Note that the hub 842 and the shaft 841 may be defined bya single member if so desired.

The rotor magnet 843 is fixed to the hub 842. The rotor magnet 843 isannular in shape and centered on the central axis 809. That is, therotor magnet 843 is arranged around the central axis 809. An innercircumferential surface of the rotor magnet 843 is arranged radiallyopposite the tooth portions 837 b and the coils 838 with a gaptherebetween. In addition, the inner circumferential surface of therotor magnet 843 defines a pole surface on which north and south polesalternate with each other.

When the three-phase drive currents are supplied to the coils 838 of thespindle motor 802 through the circuit board 833, radial magnetic flux isgenerated about the tooth portions 837 b of the stator core 837. As aresult, an interaction between the magnetic flux about the toothportions 837 b and magnetic flux from the rotor magnet 843 produces acircumferential torque which causes the rotating portion 804 to rotateabout the central axis 809 with respect to the stationary portion 803.The disk 812 supported by the hub 842 rotates about the central axis 809together with the shaft 841 and the hub 842.

Next, the structures of the thrust yoke 834 and the insulation sheet 835according to the present preferred embodiment will now be described inmore detail below. FIG. 14 is a partial vertical cross-sectional view ofthe spindle motor 802, illustrating the thrust yoke 834 and theinsulation sheet 835 among other components.

As illustrated in FIG. 14, the thrust yoke 834 preferably includes aplate portion 834 a and a projecting portion 834 b. The plate portion834 a preferably includes an annular portion fixed to the upper surfaceof the bottom portion 831 b of the base member 831. The projectingportion 834 b includes a portion extending upward from an outer edgeportion of the plate portion 834 a. The thrust yoke 834 has a highdegree of rigidity at and near an outer edge portion thereof due to theprojecting portion 834 b.

The plate portion 834 a is provided substantially in the shape of asheet with a small axial dimension. Accordingly, a space required insidethe accommodating portion 831 e of the base member 831 to accommodatethe thrust yoke 834 only needs to have a small axial dimension. Thiscontributes to further reduction of the total axial thickness of thespindle motor 802.

The insulation sheet 835 preferably includes a sheet body portion 835 aand a cover portion 835 b. The sheet body portion 835 a includes anannular portion placed on the upper surface of the bottom portion 831 bof the base member 831. The sheet body portion 835 a is arrangedradially inward of the thrust yoke 834 and axially between the bottomportion 831 b and the coils 838. The cover portion 835 b is positionedradially outward of the sheet body portion 835 a, and spaced from thebottom portion 831 b of the base member 831.

The cover portion 835 b is arranged to extend from an outer edge portionof the sheet body portion 835 a to a space above a radially inner edgeportion 834 c of the thrust yoke 834. That is, a portion of the coverportion 835 b is arranged to cover an upper surface of the edge portion834 c of the thrust yoke 834. In addition, in the present preferredembodiment, the cover portion 835 b is arranged in contact with the edgeportion 834 c of the thrust yoke 834. The edge portion 834 c isaccordingly held between the bottom portion 831 b of the base member 831and the cover portion 835 b of the insulation sheet 835.

While magnetic attraction between the thrust yoke 834 and the rotormagnet 843 induces an upward displacement of the edge portion 834 c ofthe thrust yoke 834, the cover portion 835 b provides a downwardreaction to the edge portion 834 c. This downward reaction contributesto preventing the upward displacement of the edge portion 834 c of thethrust yoke 834.

Because the plate portion 834 a of the thrust yoke 834 is in the shapeof a sheet with a small axial dimension, the plate portion 834 a of thethrust yoke 834 is especially subject to partial bending. Therefore, ifthe cover portion 835 b were not provided and the adhesive were notarranged to spread up to a lower surface of the edge portion 834 c ofthe thrust yoke 834, the edge portion 834 c of the thrust yoke 834 mightbe easily displaced upward. In the present preferred embodiment, thecover portion 835 b of the insulation sheet 835 contributes topreventing such an upward displacement of the edge portion 834 c of thethrust yoke 834. That is, the spindle motor 802 achieves a reduction inthe axial thickness thereof with the use of the thrust yoke 834 in theshape of a sheet therein, while at the same time the upward displacementof the edge portion 834 c of the thrust yoke 834 is sufficientlyprevented.

Moreover, in the present preferred embodiment, it is not necessary toprovide an additional component separate from the insulation sheet 835to prevent the upward displacement of the thrust yoke 834. An increasein the number of components of the spindle motor 802 is thus avoided.This contributes to further reducing the axial thickness of the spindlemotor 802.

The sheet body portion 835 a of the insulation sheet 835 is arrangedbetween the coils 838 and the bottom portion 831 b of the base member831. Preferably, a lower surface of the sheet body portion 835 a isarranged in contact with the upper surface of the bottom portion 831 bof the base member 831, while an upper surface of the sheet body portion835 a is arranged in contact with the coils 838. This arrangementcontributes to preventing an upward displacement of the insulation sheet835. This in turn contributes to further preventing the upwarddisplacement of the edge portion 834 c of the thrust yoke 834.Furthermore, the bottom portion 831 b of the base member 831, theinsulation sheet 835, and the coils 838 are arranged compactly in theaxial direction. This contributes to further reducing the axialthickness of the spindle motor 802.

The through hole 831 f, which extends in the axial direction, is definedin the bottom portion 831 b of the base member 831. The through hole 831f is positioned below the coils 838. The insulation sheet 835 hasdefined therein an opening portion 835 c in communication with thethrough hole 831 f. Moreover, the insulation sheet 835 includes a sheettubular portion 835 d, which is cylindrical in shape and arranged toextend downward from a periphery of the opening portion 835 c. The sheettubular portion 835 d is positioned within the through hole 831 f of thebase member 831.

The through hole 831 f is sealed with an adhesive 839, so that aninterior space of the apparatus housing is isolated from an exteriorspace. The adhesive 839 is arranged also to fix the sheet tubularportion 835 d of the insulation sheet 835 to the base member 831. Thefixing of the insulation sheet 835 to the base member 831 contributes topreventing the upward displacement of the insulation sheet 835. This inturn contributes to further preventing the upward displacement of theedge portion 834 c of the thrust yoke 834.

The insulation sheet 835 is fixed to the base member 831 through theadhesive 839 held within the through hole 831 f. In the presentpreferred embodiment, the adhesive 839 does not intrude between theupper surface of the bottom portion 831 b of the base member 831 and thelower surface of the sheet body portion 835 a of the insulation sheet835. This contributes to further reducing the axial thickness of thespindle motor 802.

Furthermore, the entire insulation sheet 835 is arranged radially inwardof the inner circumferential surface of the rotor magnet 843. That is,the insulation sheet 835 is arranged so as not to overlap with the rotormagnet 843 in the axial direction. Therefore, even if the cover portion835 b of the insulation sheet 835 is bent upward, this does not lead toa contact between the insulation sheet 835 and the rotor magnet 843.Moreover, because there is no possibility that the insulation sheet 835and the rotor magnet 843 will make contact with each other, there is noneed to provide large axial clearance between the insulation sheet 835and the rotor magnet 843. This contributes to further reducing the axialthickness of the spindle motor 802.

The thrust yoke 834 according to the present preferred embodiment has amechanism to improve the strength with which the thrust yoke 834 isfixed to the base member 831. FIG. 15 is a partial top view of thethrust yoke 834. FIG. 16 is a partial vertical cross-sectional view ofthe stationary portion 803, illustrating an elastic section 834 f of thethrust yoke 834 among other components.

As illustrated in FIGS. 15 and 16, the thrust yoke 834 includes a fixingportion 834 d. The fixing portion 834 d preferably includes a pair ofnotch portions 834 e defined in the projecting portion 834 b, and theelastic section 834 f defined between the pair of notch portions 834 e.The elastic section 834 f is arranged to extend radially outward fromthe outer edge portion of the plate portion 834 a while curving upward.A radially outer end portion of the elastic section 834 f is positionedradially outward of an outer edge portion of the projecting portion 834b. The elastic section 834 f is capable of bending in response to astress received through the radially outer end portion thereof. That is,the elastic section 834 f has flexibility.

The wall portion 831 c of the base member 831 preferably includes acylindrical surface 831 g arranged opposite an outer circumferentialsurface of the thrust yoke 834. The cylindrical surface 831 gcorresponds to an example wall surface according to a preferredembodiment of the present invention. When the thrust yoke 834 is pressfitted to the cylindrical surface 831 g of the wall portion 831 c, theelastic section 834 f is brought into contact with the cylindricalsurface 831 g, and is bent radially inward. Resultant radial forcesapplied between the elastic section 834 f and the cylindrical surface831 g cause the thrust yoke 834 to be securely fixed to the base member831.

In order to obtain a high fixing strength as a result of the pressfitting, it is preferable that a radial press-fit interference(allowance) for the press fitting of the thrust yoke 834 to the basemember 831 be about 10 μm or more, more preferably about 20 μm or more,for example. Moreover, the radial press-fit interference for the pressfitting of the thrust yoke 834 to the base member 831 is preferablyabout 200 μm or less, more preferably about 100 μm or less, for example,for increased ease of the press fitting.

More specifically, the elastic section 834 f has a corner portion 834 gthereof, i.e., a portion thereof positioned between an upper surfacethereof and an outer circumferential surface thereof, arranged incontact with the cylindrical surface 831 g of the base member 831. Thecorner portion 834 g is pressed against the cylindrical surface 831 gthrough an elastic force of the elastic section 834 f. When an upwardforce is applied to the thrust yoke 834, the elastic contact of thecorner portion 834 g with the cylindrical surface 831 g contributes topreventing an upward movement of the thrust yoke 834. An upper endportion of the cylindrical surface 831 g, which corresponds to the wallsurface, is preferably positioned at a level higher than at least thatof the corner portion 834 g. More preferably, the upper end portion ofthe cylindrical surface 831 g is positioned at a level higher than thatof an upper end portion of a portion of the projecting portion 834 bexcluding the elastic section 834 f. This arrangement allows the cornerportion 834 g to be brought into contact with the cylindrical surface831 g to further prevent the upward movement of the thrust yoke 834.

When the thrust yoke 834 is fixed to the base member 831, the elasticsection 834 f is bent to an extent according to the dimensions of thecylindrical surface 831 g of the base member 831. This allows a decreasein a required precision of the dimensions of the cylindrical surface 831g of the base member 831 as compared to when the thrust yoke 834 to bepress fitted to the base member 831 is not provided with the elasticsection 834 f.

In addition, in the present preferred embodiment, the upper end portionof the elastic section 834 f (h2) is positioned at a level lower thanthat of the upper end portion of the portion of the projecting portion834 b (h1) excluding the elastic section 834 f (h2<h1). This arrangementmakes it easy, when press fitting the thrust yoke 834 to the base member831, to press the upper end portion of the portion of the projectingportion 834 b excluding the elastic section 834 f without pressing theelastic section 834 f. This makes it possible to fit the thrust yoke 834to the base member 831 without applying an excessive downward externalforce to the elastic section 834 f.

In the present preferred embodiment, the elastic section 834 f isdefined between the pair of notch portions 834 e. This enables theelastic section 834 f to have sufficient radial dimensions to exhibitsufficient flexibility, without making the elastic section 834 fexcessively protrude radially outward, and also makes it possible toallow only the elastic section 834 f to bend while preventing otherportions of the thrust yoke 834 from being deformed.

Furthermore, in the present preferred embodiment, a radially inner endportion of each notch portion 834 e is positioned radially inward of theouter edge portion of the plate portion 834 a. This makes it possible tocheck a state of the fixing of the plate portion 834 a to the bottomportion 831 b of the base member 831. For example, it makes it possibleto check whether there is a gap between the bottom portion 831 b and theplate portion 834 a, a state of an adhesive applied between the bottomportion 831 b and the plate portion 834 a, and the like.

The elastic section 834 f is preferably arranged radially outward of therotor magnet 843. This allows an upper surface of the plate portion 834a, which is positioned radially inward of the notch portions 834 e ofthe thrust yoke 834, to be arranged axially opposite the lower surfaceof the rotor magnet 843. This contributes to improving the axialdirectivity of the magnetic attraction generated between the rotormagnet 843 and the thrust yoke 834.

Note that the fixing portion 834 d may be provided either at only onelocation or a plurality of locations in the thrust yoke 834. Note,however, that provision of the fixing portion 834 d at two or morelocations, more preferably at three or more locations, in the thrustyoke 834 will lead to an improved precision of the relative position ofthe thrust yoke 834 with respect to the central axis 809.

In addition, an adhesive 862 is arranged between the base member 831 andthe thrust yoke 834. The adhesive 862 contributes to the strength withwhich the base member 831 and the thrust yoke 834 are fixed to eachother. That is, in the present preferred embodiment, the base member 831and the thrust yoke 834 are fixed to each other by a combination of thepress fitting and the adhesive 862, for example. Accordingly, the basemember 831 and the thrust yoke 834 are fixed to each other more securelythan when they are fixed to each other by only one of the press fittingand the adhesive 862.

The adhesive 862 may deteriorate with long-term use, due to influence ofchanges in ambient temperature and the like, resulting in a decrease inthe fixing strength. In the present preferred embodiment, however, aportion of the fixing strength owing to the press fitting is maintainedeven after the deterioration of the adhesive 862. This contributes toreducing the probability of the thrust yoke 834 coming off the basemember 831 due to the magnetic attraction between the thrust yoke 834and the rotor magnet 843 after the deterioration of the adhesive 862.

Moreover, in the present preferred embodiment, a fixing strengthrequired for the fixing of the thrust yoke 834 to the base member 831does not need to be accomplished by only the adhesive 862. This leads toan increased number of options for the choice of the adhesive 862. Itmakes it possible, for example, to choose as the adhesive 862 anadhesive that takes a relatively long time to solidify, in order tofacilitate an operation of application of the adhesive 862.

Moreover, in the present preferred embodiment, the elastic section 834f, which is a portion of the projecting portion 834 b, is press fittedto the cylindrical surface 831 g of the base member 831. Therefore, astress applied from the cylindrical surface 831 g during the pressfitting is unlikely to reach the plate portion 834 a of the thrust yoke834. This reduces the probability of a deformation of the plate portion834 a. This in turn reduces the probability that the axial distancebetween the plate portion 834 a and the rotor magnet 843 will vary atdifferent positions.

Next, various example of a modifications of the second preferredembodiment will now be described below with a focus on differences fromthe above-described preferred embodiment.

FIG. 17 is a partial vertical cross-sectional view of a stationaryportion 903 according to an example of a modification of the secondpreferred embodiment. In the example of a modification illustrated inFIG. 17, a groove 956 is defined between a bottom portion 931 b and awall portion 931 c of a base member 931. A radially outer end surface ofthe groove 956 includes an axially extending cylindrical surface 931 g.Moreover, in the example of a modification illustrated in FIG. 17, aprojecting portion 934 b of a thrust yoke 934 is arranged to extenddownward from a radially outer edge portion of a plate portion 934 a.Accordingly, a plurality of elastic sections 934 f are also arranged toextend downward from the radially outer edge portion of the plateportion 934 a. The projecting portion 934 b of the thrust yoke 934 ispress fitted to the base member 931 with the elastic sections 934 farranged in contact with the cylindrical surface 931 g.

FIG. 18 is a partial vertical cross-sectional view of a stationaryportion 1003 according to another example of a modification of thesecond preferred embodiment. In the example of a modificationillustrated in FIG. 18, a groove 1056 is defined in a bottom portion1031 b of a base member 1031. A radially inner end surface of the groove1056 includes an axially extending cylindrical surface 1031 g. Moreover,in the example of a modification illustrated in FIG. 18, a projectingportion 1034 b of a thrust yoke 1034 is arranged to extend downward froma radially inner edge portion of a plate portion 1034 a of the thrustyoke 1034. Accordingly, a plurality of elastic sections 1034 f are alsoarranged to extend downward from the radially inner edge portion of theplate portion 1034 a. The projecting portion 1034 b of the thrust yoke1034 is press fitted to the base member 1031 with the elastic sections1034 f arranged in contact with the cylindrical surface 1031 g.

In the case where the projecting portion is arranged to project downwardfrom the plate portion as in the example of a modifications illustratedin FIGS. 17 and 18, an increase inflexibility in the arrangement ofother members above the thrust yoke and in the design of the dimensionsof such other members is achieved. In that case, it is easy to arrangethe rotor magnet of the rotating portion close to the plate portion ofthe thrust yoke, for example. Moreover, in the example of amodifications illustrated in FIGS. 17 and 18, an adhesive may be heldwithin the groove of the base member to achieve an increase in thefixing strength by the adhesive.

Note that each elastic section may not necessarily be arranged to extendin a single direction after projecting from the plate portion. Forexample, the elastic section may be provided with one or more bentportions in a vertical cross-section in order to improve the elasticforce of the elastic section. That is, the elastic section is onlyrequired to include a portion projecting from the plate portion in theaxial direction.

Also note that the projecting portion of the thrust yoke may besubstantially in the shape of a cylinder as in the above-describedpreferred embodiments, and that the projecting portion of the thrustyoke may alternatively be defined by one or more axial projectionsprovided at one or more circumferential positions. For example, theprojecting portion of the thrust yoke may be defined by only one or moreelastic sections. Also note that the wall surface of the base member maybe a cylindrical surface as in the above-described preferredembodiments, and that the wall surface of the base member mayalternatively be defined by one or more surfaces provided at one or morecircumferential positions.

Also note that the thrust yoke may be fixed to the base member throughonly press fitting, without the use of an adhesive.

In spindle motors according to preferred embodiments of the presentinvention, the rotor magnet may be arranged radially outward of thestator unit as in the above-described preferred embodiments, oralternatively, the rotor magnet may be arranged radially inward of thestator unit.

Note that various preferred embodiments of the present invention arealso applicable to spindle motors designed to rotate other types ofdisks than magnetic disks, e.g., an optical disk, as well as to diskdrive apparatuses including such a spindle motor.

Also note that features of the above-described preferred embodiments andthe above-described examples of modifications thereof may be combined asappropriate insofar as their features will not interfere with eachother.

Also note that, in modifications of any of the above-described preferredembodiments and the above-described examples of modifications thereof,the insulation sheet and the coils may have an axial gap therebetween.

The present invention is applicable to spindle motors and disk driveapparatuses.

Only selected preferred embodiments have been chosen to illustrate thepresent invention. To those skilled in the art, however, it will beapparent from the foregoing disclosure that various changes andmodifications can be made herein without departing from the scope of thepresent invention as defined in the appended claims. Furthermore, theforegoing description of the preferred embodiments according to thepresent invention is provided for illustration only, and not forlimiting the invention as defined by the appended claims and theirequivalents.

What is claimed is:
 1. A spindle motor comprising: a stationary portion;and a rotating portion arranged to rotate with respect to the stationaryportion; wherein the rotating portion includes a magnet arranged arounda central axis extending in a vertical direction; the stationary portionincludes: a base member; and a magnetic member arranged below the magnetand fixed to the base member; the base member includes: an upper surfaceextending out perpendicularly or substantially perpendicularly to thecentral axis; and a wall surface extending in an axial direction; themagnetic member includes: an annular plate portion arranged on the uppersurface of the base member; and a projecting portion arranged to extenddownward from the plate portion; at least a portion of the projectingportion is in contact with the wall surface; and the stationary portionfurther includes an adhesive arranged between the plate portion and theupper surface of the base member and between the projecting portion andthe wall surface.
 2. The spindle motor according to claim 1, wherein theadhesive extends to a radially outer end portion of the plate portion.3. The spindle motor according to claim 2, wherein the adhesive extendsto a lower end portion of the projecting portion.
 4. The spindle motoraccording to claim 3, wherein the adhesive is arranged to cover thelower end portion of the projecting portion.
 5. The spindle motoraccording to claim 3, wherein the adhesive is arranged to extendcontinuously from the radially outer end portion of the plate portion tothe lower end portion of the projecting portion.
 6. The spindle motoraccording to claim 1, wherein the adhesive is arranged to contact alower end portion of the projecting portion.
 7. The spindle motoraccording to claim 6, wherein the adhesive is arranged to cover thelower end portion of the projecting portion.
 8. The spindle motoraccording to claim 1, wherein the base member includes an inclinedsurface defined between the upper surface and the wall surface; and theadhesive is arranged between the inclined surface and a portion of themagnetic member that is opposed to the inclined surface.
 9. The spindlemotor according to claim 8, wherein the adhesive is arranged to extendfrom a gap between the plate portion and the upper surface of the basemember to a gap between the projecting portion and the wall surfacethrough a gap between the inclined surface and the portion of themagnetic member which is opposed to the inclined surface.
 10. Thespindle motor according to claim 1, wherein the upper surface of thebase member includes a metal surface exposed at least at a portionthereof positioned below the plate portion; and the adhesive is arrangedbetween the plate portion and the exposed metal surface of the uppersurface.
 11. The spindle motor according to claim 10, wherein the wallsurface of the base member includes an exposed metal surface; and theadhesive is arranged between the projecting portion and the exposedmetal surface of the wall surface.
 12. The spindle motor according toclaim 1, wherein the wall surface of the base member includes an exposedmetal surface; and the adhesive is arranged between the projectingportion and the exposed metal surface of the wall surface.
 13. Thespindle motor according to claim 1, wherein the projecting portionincludes a raised portion defined in an outer circumferential surface oran inner circumferential surface of the projecting portion; and theraised portion is arranged to be in contact with the wall surface. 14.The spindle motor according to claim 13, wherein a plurality of raisedportions are provided, and the raised portions are arranged along acircumferential direction.
 15. The spindle motor according to claim 13,wherein the raised portion includes a curved surface.
 16. The spindlemotor according to claim 13, wherein the projecting portion furtherincludes a concave portion defined in a surface thereof opposite to thesurface thereof in which the raised portion is defined, the concaveportion being defined at a position corresponding to the raised portion.17. The spindle motor according to claim 1, wherein the base memberincludes a groove arranged to have the projecting portion accommodatedtherein; and the adhesive is arranged in the groove.
 18. The spindlemotor according to claim 1, wherein the stationary portion includes aplurality of coils; and an inner circumferential surface of theprojecting portion is arranged radially inward of an innercircumferential surface of the magnet and radially outward of the coils.19. The spindle motor according to claim 1, wherein an outercircumferential surface of the plate portion is arranged radiallyoutward of an outer circumferential surface of the magnet.
 20. A diskdrive apparatus comprising: the spindle motor of claim 1; an accessportion arranged to perform at least one of reading and writing ofinformation from or to a disk held by the rotating portion of thespindle motor; and a housing arranged to contain the spindle motor andthe access portion.